Sooty spark plugs

[aclam]

I have a 1999 Evenrude 90 fitch - all 4 plugs are very badly sooted up, she sounds like she is missing on just 1 cylinder through out the rev range.
Any ideas what is causing the carbon, could it be the choke is not coming fully off?

 

[seahorse5]

Re: Sooty spark plugs

Soot covered plugs on an older FICHT motor is normal. At high speeds they clean off and are usually a nice tan, but as soon as the motor slows down below about 1800rpm, the combustion process changes to the lean burn mode and the plugs will soot up.